Metal lines are commonly used for connecting circuits in printed circuit boards and multichip modules. Existing metal line deposition techniques include laser chemical vapor deposition and laser deposition from metal precursors. These techniques, however, have certain disadvantages associated with them. Chemical vapor deposition processes require toxic gases and a vacuum chamber. Deposition from metal precursors requires wet processing that can damage or introduce defects in the surrounding circuitry.
A less expensive and more environmentally friendly metal deposition technique is laser ablation. Laser ablation of metal films in general is a known technique wherein a laser beam is focused onto the metal film. The heat and shock wave generated by the laser beam remove, or discharge, particles of the film. Thin films of metals such as copper, gold, silver and aluminum may be easily removed, or ablated, using green light lasers, such as Q-switched doubled Nd:YAG, Nd:YLF, or copper vapor lasers.
One such laser ablation technique involves the use of pulsed-laser deposition in order to layer complex thin films on substrates. Using this technique, a focused laser beam is directed onto a target film at an angle. The plume of particles that are ablated from the film land on a substrate that is positioned parallel to the target. The particles are thus deposited onto the substrate to form a thin epitaxial coating. Both the substrate and the target are contained in a vacuum environment in this technique. This technique is useful for coating wide surfaces but not localized conductive metal lines. When using this technique for depositing metal lines, as the particles are deposited onto the substrate, the particles are not confined to the area of the metal line. This results in deposition of metal droplets and mist outside the area defined for the metal line.